Aromatic Hydrocarbon

To determine the correct answer to the question, let's examine both the assertion and the reason provided:

Assertion A: [6] Annulene, [8] Annulene, and cis-[10] Annulene, are respectively aromatic, non-aromatic, and aromatic.

Reason R: Planarity is one of the requirements of aromatic systems.

1. Analyzing Assertion A:
   • [6] Annulene: This molecule is aromatic because it satisfies the Huckel's rule for aromaticity, which requires the molecule to have π electrons, where is a non-negative integer. Here, for [6] annulene, (as it has π electrons).
   • [8] Annulene: This molecule is non-aromatic. According to Huckel's rule, it would require 10 π electrons to be aromatic, but it only has 8, which does not satisfy the rule.
   • cis-[10] Annulene: This molecule is also non-aromatic because it cannot maintain planarity due to angle strain and steric hindrance. Although it has 10 π electrons, its inability to be planar disqualifies it as aromatic.
2. Analyzing Reason R:

Planarity is indeed one of the critical requirements for a compound to exhibit aromaticity. Aromatic compounds must have a cyclic, continuous overlap of p orbitals, which is only possible if the molecule is planar.

1. Conclusion: Since Assertion A is incorrect but Reason R is correct, the correct option is: A is not correct but R is correct.

- Hoffmann Degradation Reaction: This reaction uses Br2 and NaOH to convert amides into amines. Reagent: (III).
- Clemenson Reduction: This reaction reduces ketones or aldehydes to alkanes using Zn-Hg in HCl. Reagent: (IV).
- Cannizzaro Reaction: This reaction involves disproportionation of aldehydes without α-hydrogen in concentrated alkali. Reagent: (I).
- Reimer-Tiemann Reaction: This reaction introduces a −CHO group to phenols using CHCl₃ and NaOH. Reagent: (II).

Chirality in coordination complexes occurs when the complex lacks a plane of symmetry.
- For the given complexes:
cis–[PtCl (en) ] : The cis arrangement of ethylene diamine (en) ligands around the Pt center creates a chiral structure.
trans–[PtCl (en) ] : The trans arrangement is symmetric, making the complex achiral.
cis–[PtCl (NH ) ]: The complex has a plane of symmetry and is not chiral.
trans–[Co(NH ) Cl ] : The trans arrangement of ligands makes the complex symmetric and achiral.
Final Answer: (1) cis–[PtCl (en) ] .